Method and system for pressure harvesting for underwater unmanned vehicles

ABSTRACT

An underwater vehicle includes systems for harvesting ambient hydrostatic pressure and storing the same as a gas pressure in a compressed gas system and as a water pressure in a pressurized electrolysis system. The gas pressure is used to perform mechanical work or to generate electrical power via a prime mover. The water pressure is used to release pressurized hydrogen and oxygen gases via electrolysis. The pressurized hydrogen and oxygen gases are used in a combustion chamber to generate propulsion power for the underwater vehicle.

FIELD OF INVENTION

The present invention relates generally to power generation and propulsion systems, and more particularly, to power generation and propulsion by harvesting hydrostatic pressure.

BACKGROUND

Undersea Unmanned Vehicles (UUVs) are utilized for a variety of applications including both commercial and military operations. However, providing such vehicles with sufficient fuel and/or power storage means necessary to propel the UUV and its payload for extended periods of time have been problematic.

High-speed sprint capabilities in UUVs may also be desirable for various applications, for example, for military applications. Underwater rocket engines and impulse water-jet engines may be used in UUVs for achieving high-speed sprints. Impulse water-jet engines use hydrogen and oxygen gases as fuel to propel the UUVs. However, hydrogen and oxygen gases need to be pressurized above the ambient hydrostatic pressure for effective operation of the impulse water-jet engines. For example, if a UUV is at a depth of about 800 meters (m), the ambient hydrostatic pressure may be about 80 atm. Pressurization of hydrogen and oxygen gases to a pressure greater than 80 atmospheric pressure (atm) in a UUV using conventional compressor systems may be so energy-intensive as to render such systems impractical. Improved power generation and sprint-propulsion systems for UUVs would prove beneficial.

SUMMARY

As described herein, a method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle includes the step of pressurizing a gas in a first gas tank in the underwater vehicle using a high ambient hydrostatic pressure encountered by the underwater vehicle during a submerged state of the underwater vehicle within a body of water. At least some of the pressurized gas is transferred from the first gas tank to a second gas tank in the underwater vehicle. At least some amount of the pressurized gas is transferred from the second gas tank to a prime mover in the underwater vehicle for performing mechanical work. The method further includes the step of storing the gas expressed by the prime mover in a third gas tank in the underwater vehicle. At least some amount of gas is transferred from the third gas tank to the first gas tank in the underwater vehicle using a low ambient hydrostatic pressure encountered by the underwater vehicle during the submerged state in the water body.

According to another embodiment of the invention, a compressed gas system for harvesting ambient hydrostatic pressure for an underwater vehicle operative to descend within a water body to a given depth and to ascend from the given depth of the water body to a lesser depth cyclically or in an alternating fashion includes a first gas tank and a second gas tank in fluid communication with the first gas tank. A third gas tank is in fluid communication with the second gas and the first gas tank. A first valve controls a gas flow between the second gas tank and the third gas tank. A second valve controls a gas flow between the third gas tank and the first gas tank. The gas stored in the third gas tank is selectively subjectable to the ambient hydrostatic pressure during a submerged state of the underwater vehicle within the water body.

According to an embodiment of the invention, the compressed gas system further includes a first differential valve operatively coupled to the third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank to selectively subject the gas stored in the third gas tank to the ambient hydrostatic pressure. A second differential valve operatively coupled to the third gas tank is configured to be selectively actuated when the ambient hydrostatic pressure is higher than the gas pressure in the third gas tank to selectively subject the gas stored in the third gas tank to the ambient hydrostatic pressure.

According to an embodiment of the invention, the compressed gas system further includes a first heat exchanger configured to extract heat energy from the gas stored in the first gas tank, and a second heat exchanger configured to transfer heat energy into the gas stored in the second gas tank.

According to an embodiment of the invention, a method for pressurized electrolysis of fresh water in an underwater vehicle includes the step of storing fresh water in a first water tank in the underwater vehicle. The fresh water in the first water tank is pressurized using the ambient hydrostatic pressure when the underwater vehicle is in a submerged state within a water body. The pressurized water is electrolyzed to release hydrogen and oxygen gases. The method further includes the step of storing the released hydrogen gas and the oxygen gas in a first hydrogen tank and a first oxygen tank respectively.

According to an embodiment of the invention, the method further includes the step of cooling the stored hydrogen gas in the first hydrogen tank, thereby reducing the pressure of the stored hydrogen gas in the first hydrogen tank. The method also includes the step of cooling the stored oxygen gas in the first oxygen tank, thereby reducing the pressure of the stored oxygen gas in the first oxygen tank.

In an embodiment of the invention, the method further includes the steps of pressurizing the fresh water stored in the first water tank using the ambient hydrostatic pressure and transferring the pressurized water from the first water tank to a second water tank. The hydrogen gas and the oxygen gas released in the electrolyzing step are stored in a second hydrogen tank and a second oxygen tank, respectively, before storing the hydrogen gas and the oxygen gas in the first hydrogen tank and the first oxygen tank, respectively. The method includes the steps of pressurizing the hydrogen gas and the oxygen gas stored in the second hydrogen tank and the second oxygen tank respectively using the ambient hydrostatic pressure in the submerged state of the underwater vehicle within the water body and transferring the pressurized hydrogen gas and the oxygen gas from the second hydrogen tank and the second oxygen tank, respectively, to the first hydrogen tank and the first oxygen tank, respectively.

According to an embodiment of the invention, the method further includes the step of heating the stored hydrogen gas and the stored oxygen gas in the first hydrogen tank and the first oxygen tank respectively, thereby increasing the pressures of the stored hydrogen gas and the stored oxygen gas in the respective first tanks. According to an embodiment, the heating step includes transferring of at least some quantity of heat energy to the first hydrogen tank and the first oxygen tank from a combustor, wherein the pressurized hydrogen gas and the pressurized oxygen gas are combusted.

According to an embodiment of the invention, a system for pressurized electrolysis of fresh water in an underwater vehicle includes a first fresh water tank and an electrolyzer in fluid communication with the first fresh water tank. The electrolyzer is configured to electrolyze fresh water to release hydrogen and oxygen gases. The system further includes a first hydrogen tank and a first oxygen tank in fluid communication with the electrolyzer for, respectively, storing the hydrogen gas and the oxygen gas released by the electrolyzer. A first pressure transfer system is adapted to exert the ambient hydrostatic pressure on the water stored in the first fresh water tank.

According to an embodiment of the invention, the system further includes a first one-way differential valve interposed between the electrolyzer and the first hydrogen tank to regulate the flow of the hydrogen from the first hydrogen tank to the electrolyzer. A second one-way differential valve is interposed between the electrolyzer and the first oxygen tank to regulate the flow of the oxygen from the first oxygen tank to the electrolyzer.

According to an embodiment of the invention, the pressurized electrolysis system further includes a second fresh water tank in fluid communication with the first fresh water tank via a third one-way differential valve, and with the electrolyzer via a first valve. A second hydrogen tank is in fluid communication with the electrolyzer via a second valve, and with the first hydrogen tank via the first one-way differential valve. A second oxygen tank is in fluid communication with the electrolyzer via a third valve, and with the first oxygen tank via the second one-way differential valve. A second pressure transfer system is adapted to exert the ambient hydrostatic pressure on the hydrogen stored in the second hydrogen tank in the submerged state of the underwater vehicle within the water body. A third pressure transfer system is adapted to exert the ambient hydrostatic pressure on the oxygen stored in the second oxygen tank, in the submerged state of the underwater vehicle within the water body.

According to an embodiment of the invention, the system further includes a combustor configured to receive, from the first hydrogen tank, the pressurized hydrogen gas, and, from the first oxygen tank, the pressurized oxygen gas for combustion therein.

According to an embodiment of the invention, the system further includes a heat transfer system configured to transfer at least some quantity of heat, generated in the combustor due to the combustion of the pressurized hydrogen gas and the pressurized oxygen gas therein, to the first hydrogen tank and the first oxygen tank, thereby raising the temperatures and the pressures of the pressurized hydrogen gas and the pressurized oxygen gas stored in the respective first hydrogen and oxygen tanks.

BRIEF DESCRIPTION OF THE DRAWINGS

Understanding of the present invention will be facilitated by consideration of the following detailed description of the exemplary embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and in which:

FIG. 1 is a schematic diagram for a compressed gas system in an underwater vehicle submerged in a water body for harvesting the ambient hydrostatic pressure, according to an embodiment of the invention;

FIG. 2 is a schematic diagram of a fluid decoupler of the system of FIG. 1, according to an embodiment of the invention;

FIG. 3 schematically illustrates various stages of the descent and the ascent of an UUV in a water body, harvesting the ambient hydrostatic pressure to perform mechanical work as well as to conduct pressurized electrolysis of fresh water, according to an embodiment of the invention;

FIG. 4 is a process flow for harvesting the ambient hydrostatic pressure in an underwater vehicle, according to an embodiment of the invention;

FIG. 5 is a schematic diagram for a system for pressurized electrolysis for an underwater unmanned vehicle submerged in a water body, according to an embodiment of the invention;

FIG. 6 is a schematic diagram of an impulse water-jet engine for use with the system of FIG. 5, according to an embodiment of the invention;

FIG. 7 is a process flow for a method for pressurized electrolysis in an underwater unmanned vehicle submerged in a water body, according to an embodiment of the invention; and

FIG. 8 is a schematic diagram of a system for continuous pressurized electrolysis for an underwater unmanned vehicle submerged in a water body, according to an embodiment of the invention.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in such underwater unmanned vehicles and clathrate gliders. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications known to those skilled in the art.

It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention.

One or more figures show block diagrams of systems and apparatus embodying aspects of the invention. One or more figures show flow diagrams illustrating systems and apparatus for such embodiments. However, it is to be understood that the operational and process flows described herein may be performed by embodiments of systems and apparatus other than those discussed with reference to the block diagrams, and embodiments discussed with reference to the systems/apparatus could perform operations different from those discussed with reference to the accompanying flow diagrams.

Although the following description refers to water bodies, sea, and seawater, such terms are for illustrative purposes only and are not intended to limit the scope of the invention. The compressed gas system described herein may be implemented in a system operative in any other liquid where the requisite pressure difference between the gas in the compressed gas system and the ambient pressure encountered by the system in a submerged state within a liquid body is available. Similarly, the pressurized electrolysis system described herein may be implemented in any other liquid where the requisite pressure difference between the fresh water in the water tank and the ambient pressure encountered by the system in a submerged state within a liquid body is available. The use of the terms such as “sea,” “seawater,” and “ambient water” are solely for illustrative purposes and should not be construed as limiting the scope of the invention.

In one configuration, one or both of the compressed gas system and the pressurized electrolysis system described herein may be deployed in Clathrate Powered Undersea Unmanned Vehicles (CPUUVs), such as those disclosed in the commonly owned, pending United States patent applications having Ser. No. 12/557,143, filed Sep. 10, 2009, and Ser. No. 12/017,966, filed Jan. 22, 2008, which applications are incorporated by reference herein in their entireties. It is understood that, although the following description of the various embodiments of the invention may refer to a CPUUV, the described embodiments may also be deployed in other UUVs and underwater gliders. The terms UUV and CPUUV may, therefore, be used interchangeably without limiting the scope of the disclosure. Such variations in the described embodiments are intended to be within the scope of the invention. The CPUUVs, as described in the '143 and the '966 applications, can traverse the ocean driven by a thermodynamic buoyancy modulation cycle that operates by ascending into warm surface water and descending into cold deep water, as described in further detail below. The deepest depth of the modulation cycle exceeds the depth of the known underwater sprint propulsion vehicles.

As described in detail in the '143 and the '966 applications, the CPUUV descends in a water body, as the warm surface water starts melting the clathrate ice stored in a clathrate bladder in the CPUUV. The melting of the clathrate ice in the bladder causes a contraction in the volume of the bladder. The bladder contraction in turn causes an increase in the volume of the adjacent ballast tanks, which then receive ambient seawater. As the CPUUV stores the seawater in the ballast tanks, its buoyancy decreases causing the CPUUV to descend into the water body. At the conclusion of its descent, the CPUUV is surrounded by relatively cold ambient seawater. The relatively cold ambient seawater is utilized to extract heat from the molten clathrate ice in the clathrate bladder, thereby initiating the freezing of the clathrate in the bladder. As the clathrate ice freezes, its volume increases, thereby expanding the clathrate bladder. The expansion of the clathrate bladder causes the seawater stored in the ballast tanks to be expelled. As the seawater is expelled from the ballast tanks, the buoyancy of the CPUUV increases. As its buoyancy increases, the CPUUV starts its ascent in the water body. When the CPUUV culminates its ascent, the clathrate in the clathrate bladder has reverted to its frozen state. The CPUUV is now surrounded by relatively warm surface water again, ready to initiate its descent after the warm surface water is permitted to substantially melt the frozen clathrate ice or hydrate in the clathrate bladder. Thus, the buoyancy of the CPUUV is modulated thermodynamically by utilizing the difference in temperatures of the ambient seawater at the surface, which temperature is generally higher than the melting temperature of the clathrate and the temperatures of the ambient seawater at the depths, where the temperatures are generally lower than the freezing point of the clathrate.

Compressed Gas System for Harvesting Ambient Hydrostatic Pressure

Referring to FIG. 1, a compressed gas system 100 for harvesting ambient hydrostatic pressure for use in an UUV is schematically illustrated. In an embodiment of the invention, system 100 includes a high pressure gas tank 130, a low pressure gas tank 110, a recirculation or intermediate gas tank 120, a prime mover 140, a device 180, a controller 170, and a plurality of sensors 190. A heat exchanger 112 is in thermal communication with low pressure gas tank 110. A heat exchanger 132 is in thermal communication with high pressure gas tank 130. In an exemplary embodiment, high pressure gas tank 130, low pressure gas tank 110 and recirculation gas tank 120 may all be fabricated from similar materials and may have similar dimensions. It will be understood that the qualifiers “high pressure,” “low pressure” and “intermediate pressure” are used to describe tanks 130, 110, 120, respectively, for the ease of understanding and should not be construed as any limitations on the characteristics of gas tanks 130, 110, 120.

Prime mover 140 drives a device 180, which device 180 may take the form of any of device which may be driven by prime mover 140. Some non-limiting examples of device 180 are briefly discussed below. The term “prime mover” is intended to cover any machine, such as, but not limited to, a turbine that transforms pressure energy of a fluid (e.g., a gas) to mechanical work or electrical energy. Other non-limiting examples of prime mover 140 include a rudder driver, which may include a gas cylinder and a piston that drives a rod to drive a rudder (an example of device 180) or a control surface such as a submarine foil (another example of device 180) for controlling the UUV's degrees of freedom during the UUV's operation in the water body; a mass balance driver, which may include a mass on a screw (yet another example of device 180) that is driven by a compressed gas piston and a cam for adjusting the center of gravity of the UUV; a ballast regulator, which may include a gas bladder (yet another example of device 180) in a ballast tank for driving the ballast; a maneuvering thruster, which may include a gas bladder in a small ballast tank having a fixed nozzle for creating, for example, a water jet; a micro-turbine configured to power a generator; a micro-turbine for powering a propeller; and a micro-turbine for powering a seawater impellor configured to pump seawater over a heat exchanger.

High pressure gas tank 130 is in fluid communication with prime mover 140 through a control or check valve 135. Control valve 135 may be selectively actuated to control the flow of a pressurized gas from high pressure gas tank 130 to prime mover 140. For instance, if the gas pressure exceeds a predetermined pressure threshold in high pressure gas tank 130, valve 135 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the pressurized gas to flow from high pressure gas tank 130 to prime mover 140. Prime mover 140 is in fluid communication with low pressure gas tank 110 such that the gas flowing out from prime mover 140 is stored in low pressure gas tank 110. Low pressure gas tank 110 is in fluid communication with recirculation or intermediate gas tank 120. A control or check valve 115 controls the flow of the gas from low pressure gas tank 110 to recirculation tank 120. For example, if the gas pressure in low pressure gas tank 110 exceeds a predetermined pressure threshold, valve 115 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the gas to flow from low pressure gas tank 110 to recirculation tank 120. Recirculation tank 120 is in fluid communication with high pressure gas tank 130. A control or check valve 125 controls the flow of the gas from recirculation tank 120 to high pressure gas tank 130. If the gas pressure in recirculation tank 120 exceeds a predetermined pressure threshold, valve 125 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the gas to flow from recirculation tank 120 to high pressure gas tank 130.

In one configuration, recirculation tank 120 is in fluid communication with a fluid decoupler 150. System 100 further includes a low pressure one-way differential valve 145 and a high pressure one-way differential valve 155 in fluid communication with fluid decoupler 150. In an embodiment of the invention, fluid decoupler 150 may take the form of a seawater bellows. In another configuration, fluid decoupler 150 and recirculation tank 120 may be combined into a unitary structure, as will be described below in further detail.

In an exemplary embodiment, heat exchanger 112 may be configured to receive ambient seawater therein to effect heat transfer between low pressure gas tank 110 and the ambient seawater. Likewise, heat exchanger 132 may be configured to receive ambient seawater therein to effect heat transfer between high pressure gas tank 130 and the ambient seawater. In another embodiment, heat exchanger 132 may be configured to collect and transfer heat, such as heat generated by the electronics present in the UUV (i.e., dissipation or “waste” heat) and transfer the same to high pressure gas tank 130 to selectively increase the temperature of the gas stored in high pressure gas tank 130. It will be understood that system 100 further includes pumps and valves for regulating the flow of coolant and/or ambient seawater through heat exchangers 112, 132. However, since such heat exchanger systems are known in the art, they are not described in further detail for the sake of brevity.

Referring also to FIG. 2, fluid decoupler 150 is schematically illustrated, according to an embodiment of the invention. Fluid decoupler 150 includes a first compartment 142, a second compartment 144 and a piston 146 in an exemplary configuration. First compartment 142 is in fluid communication with recirculation gas tank 120 in an exemplary embodiment. The gas from recirculation gas tank 120 may be received by first compartment 142, responsive to movement of piston 146. The gas from first compartment 142 may be ejected to recirculation gas tank 120, responsive to movement of piston 146. In another embodiment, first compartment 142 may serve as recirculation gas tank 120 and be in fluid communication with low pressure gas tank 110 (of FIG. 1) as well as high pressure gas tank 130 (of FIG. 1) via respective check valves 115, 125 (of FIG. 1).

Second compartment 144 is in fluid communication with high pressure differential valve 155 and low pressure differential valve 145. The ambient water, for example the seawater, may be received by second compartment 144 via high pressure differential valve 155, responsive to a difference in the pressure of the gas stored in first compartment 142 and the ambient hydrostatic pressure. Conversely, the received seawater may be ejected from second compartment 144 via low pressure differential valve 145, responsive to a difference in the pressure of the gas stored in first compartment 142 and the ambient hydrostatic pressure. Piston 146 may move responsive to the difference in the pressures of the ambient seawater and the gas stored in recirculation gas tank 120 and resulting actuation of high pressure differential valve 155 and low pressure differential valve 145 as explained below. It will be understood that piston 146 is so arranged between first compartment 142 and second compartment 144 as to substantially prevent any leakage of the gas stored in first compartment 142 into second compartment 144 as well as any leakage of the water stored in second compartment 144 into first compartment 142.

High pressure differential valve 155 serves to selectively subject the gas in the fluid decoupler 150 to an ambient hydrostatic pressure 160 (of FIG. 1) when ambient hydrostatic pressure 160 is higher than the pressure of the gas stored in recirculation gas tank 120. For example, for a UUV having system 100 of FIG. 1 embodies therein, as the UUV descends in the water body, a depth may be reached wherein the ambient hydrostatic pressure 160 (of FIG. 1) exceeds a predetermined pressure threshold. High pressure differential valve 155 may then be actuated to exert ambient hydrostatic pressure 160 (of FIG. 1) on the gas stored in first compartment 142 and/or recirculation gas tank 120. Responsive to the actuation of high pressure differential valve 155, the ambient seawater enters second compartment 144 and exerts a force, i.e., pushes, on piston 146 towards first compartment 142. The movement of piston 146 causes a reduction or contraction in the volume available to the gas stored in first compartment 142 and/or recirculation gas tank 120. Therefore, the pressure of the gas stored in first compartment 142 and/or recirculation gas tank 120 increases. Further, if valve 125 is actuated when the ambient seawater enters second compartment 144, gas may flow from recirculation gas tank 120 to high pressure gas tank 130 (of FIG. 1).

Low pressure differential valve 145, on the other hand, serves to discharge pressure from recirculation gas tank 120 via fluid decoupler 150 when ambient hydrostatic pressure 160 (of FIG. 1) is lower than the pressure of the gas stored in recirculation gas tank 120. During the ascent of the UUV with system 100 in the water body from a given depth within the water body, when ambient hydrostatic pressure 160 (of FIG. 1) falls below a predetermined pressure threshold, low pressure differential valve 145 may be actuated to depressurize the gas stored in first compartment 142 and/or recirculation gas tank 120. Since the ambient hydrostatic pressure 160 (of FIG. 1) is lower than the pressure of the gas stored in first compartment 142 and/or recirculation gas tank 120, the difference between the pressure of the gas stored in first compartment 142 and/or recirculation gas tank 120 and hydrostatic pressure 160 (of FIG. 1) causes piston 146 to move towards second compartment 144 and to push the seawater out of second compartment 144. Thus, the volume available to gas stored in first compartment 142 and/or recirculation gas tank 120 increases. Therefore, the pressure of the gas stored in first compartment 142 and/or recirculation gas tank 120 decreases. The movement of piston 146 toward second compartment 144 may also cause further flow of the gas from low pressure gas tank 110 to first compartment 142 and/or recirculation gas tank 120, if valve 115 is also actuated.

Referring again to FIG. 1, in one configuration, controller 170 may take the form of a general purpose computer. In the illustrated embodiment, controller 170 controls the operation of valves 115, 125, 135, 145 and 155. For instance, controller 170 may be in electrical communication with one or more pressure sensors, collectively illustrated as sensors 190, located in one or more of high pressure gas tank 130, low pressure gas tank 110 and recirculation gas tank 120. Controller 170 may also be in electrical communication with one or more ambient temperature sensors, depth sensors or velocity sensors, collectively illustrated as sensors 190, located externally on or outside the UUV hull. In other embodiments, one or more of valves 115, 125, 135, 145 and 155 may be self-actuating responsive to the gas pressure in system 100 and/or to the difference in the gas pressure in system 100 and ambient hydrostatic pressure 160.

An advantage of controller 170 controlling the actuation of high pressure differential valve 155 and low pressure differential valve 145 is that differential valves 155, 145 may be selectively actuated only when needed to pressurize or depressurize the gas in system 100. Mechanical self-actuating differential valves 155, 145, on the other hand, may remain actuated based on the difference in the pressures of the gas stored in first compartment 142 and/or recirculation gas tank 120, regardless of the need of the system. Such prolonged actuation of differential valves 155, 145 may expose valves 155, 145 to ambient seawater for prolonged periods of time. Increased exposure to ambient seawater may, in turn, lead to bio-fouling issues, for example. It is further understood that bio-fouling may be addressed using ozone purge or chlorine purge techniques known in the art.

Referring now to FIGS. 1 and 3, the operation of compressed gas system 100 in an UUV 330 is described. At stage A, UUV 330 is near a surface 310 of a water body, such as a sea or an ocean. High pressure gas tank 130, low pressure gas tank 110 and recirculation gas tank 120 are at least partially filled with a dense gas. In an exemplary embodiment, the dense gas may take the form an inert gas such as xenon, krypton, argon or a gas such as nitrogen. A gas having a large molecular size is suitable for system 100 because the larger molecules are less likely to leak through tank walls, the piping walls and the interfaces between the different components of system 100. Furthermore, a pressurized gas having a large molecular size imparts more force on, for example, the blades of a turbine, for a given volume of the gas. Gases that remain in gaseous state between the temperature range from about 2° Celsius (C) to about 40° C. and at pressures ranging from about 1 atmospheric pressure (atm) to several hundred atms may be used in system 100. A gas with a high compressibility factor close to unity is also advantageous for system 100. Gases that tend to become acidic or basic when exposed to water may also be used, however, such gases may require additional design adjustments to system 100 to prevent, for example, corrosion of the various gas tanks and piping of system 100.

UUV 330 starts its descent into the water body towards a bed 320 of the water body. During stage B, as UUV 330 descends further in the water body, ambient hydrostatic pressure 160 increases. Once ambient hydrostatic pressure 160 exceeds beyond a predetermined threshold, high pressure differential valve 155 is actuated. The seawater enters second compartment 144 and causes piston 146 to pressurize the gas contained in first compartment 142. As a result, the gas contained in recirculation gas tank 120 is pressurized. As the gas pressure in recirculation gas tank 120 exceeds a predetermined threshold, valve 125 is actuated to permit the flow of the gas from recirculation gas tank 120 to high pressure gas tank 130. As the mass of the gas flowing into high pressure gas tank 130 increases, the gas pressure in high pressure gas tank 130 also increases. Thus, high ambient hydrostatic pressure 160 is harvested and stored in form of the gas pressure in high pressure gas tank 130. In one configuration, once a predetermined gas pressure in high pressure gas tank 130 is achieved, valve 125 is actuated to cut off further flow of the gas from recirculation gas tank 120 to high pressure gas tank 130. Similarly, once a predetermined gas pressure in recirculation gas tank 120 is achieved, high pressure differential valve 155 is actuated to cut off further flow of the seawater into the second compartment 144. In an exemplary embodiment, controller 170 may dynamically actuate differential valves 125, 135, to optimally harvest the ambient hydrostatic pressure, based on the parameters such as the ambient hydrostatic pressure, gas pressures in low pressure gas tank 110, recirculation gas tank 120, high pressure gas tank 130, the depth of UUV 330 and the velocity of UUV 330 as measured by the respective pressure sensors, temperature sensors, the depth sensors and the velocity sensors associated with UUV 330.

According to an embodiment of the invention, a method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle thus includes a step of storing a gas at a given pressure in a first tank within the underwater vehicle. The method further includes a step of pressurizing the gas in the first tank using an ambient pressure associated with the water body encountered by the UUV when in a submerged state, wherein the ambient pressure is higher than the given pressure.

As is known in the art, for a constant volume and a constant mass, a decrease in temperature results in a decrease in the pressure of a gas, per the ideal gas law. As UUV 330 is descending during stage B, the temperature of ambient seawater surrounding UUV 330 decreases. The relatively colder ambient seawater flowing through heat exchanger 132 may be used to cool high pressure gas tank 130. The cooling of high pressure gas tank 130 results in a reduction in pressure of the gas stored therein. In an exemplary embodiment, valve 125 may be periodically actuated to permit further flow of high pressure gas from recirculation tank 120 to high pressure gas tank 130. In an embodiment, valve 125 may self-actuate, depending on the pressure difference between the gas stored in recirculation gas tank 120 and high pressure gas tank 130. In another embodiment, valve 125 may be dynamically actuated by controller 170 based on the pressures in tanks 120, 130, as measured by the respective pressure sensors associated with tanks 120, 130. Similar reduction in the pressure of the gas stored in low pressure gas tank 110 due to the cooling of low pressure gas tank 110 further enhances its capacity to receive more quantity of gas emitted from prime mover 140.

Further, when prime mover 140 is in operation, the gas expressed from prime mover 140 and received by low pressure gas tank 110, increases the pressure and the temperature of the gas stored in low pressure gas tank 110. The relatively colder ambient seawater flowing through heat exchanger 112 may be used to cool low pressure gas tank 110, to mitigate the rise in the temperature and the pressure of gas stored in low pressure gas tank 110, when prime mover 140 is in operation. Thus, the lower temperatures of ambient seawater advantageously may be used to store higher quantities of high pressure gas in high pressure gas tank 130 as well to receive higher quantities of gas in low pressure gas tank 110 during the operation of the prime mover 140. In an exemplary embodiment, controller 170 may regulate the flow of the ambient seawater in heat exchangers 112, 132 based on the temperatures of the ambient seawater, the gas stored in low pressure gas tank 110, and the gas stored in high pressure gas tank 130.

At stage C, UUV 330 reaches a target depth (e.g., the maximum design depth) in the water body. Valve 135 may be actuated to permit the flow of pressurized gas from high pressure gas tank 130 to prime mover 140. Prime mover 140 converts the pressure energy of the pressurized gas into another form of energy, for example, mechanical energy. For instance, prime mover 140 may power one or more propellers to impart motion to UUV 330. In a CPUUV, prime mover 140 powering a propeller may reduce the consumption of scarce stored electrical energy for forward propulsion. Prime mover 140 also propels the CPUUV at a speed sufficient to maintain the required flow of seawater within the CPUUV for the formation of the clathrate hydrate. Prime mover 140 may also be used to shift the center of gravity of UUV 330 to change its orientation from a nose down orientation to a horizontal orientation on reaching stage C. Prime mover 140 may also be used to pump the ambient seawater through various heat exchangers present in UUV 330, for example to cool the gas stored in high pressure gas tank 130, in an exemplary configuration.

In another configuration, prime mover 140 may convert the pressure energy of the pressurized gas into electrical energy. In an exemplary configuration, if UUV 330 includes a critical power load, such as an active sonar pulse, prime mover 140 may briefly power a generator to charge up a capacitor to store sufficient electrical energy to power the sonar amplifiers. In another embodiment, prime mover 140 may power a generator to recharge a battery (not shown). In yet another embodiment, prime mover 140 and a generator (not shown) powered therewith may supply electric energy to electrolyze pressurized fresh water to provide pressurized hydrogen and pressurized oxygen, as described further below.

The amount of power or energy generated by prime mover 140 is determined by the capacity and/or pressure characteristics of low pressure gas tank 110. The gas expressed from prime mover 140 is received by low pressure gas tank 110. As the mass of the gas flowing from high pressure gas tank 130 to prime mover 140 increases, the mass of the gas in low pressure gas tank 110 also increases, thereby increasing the gas pressure in low pressure gas tank 110. The higher the quantity of the gas low pressure gas tank 110 is able to store therein, the more the power generated by prime mover 140. Likewise, the higher the pressure low pressure gas tank 110 is able to withstand, the more the power generated by prime mover 140. Therefore, the capacity of low pressure gas tank 110 determines the amount of power or energy generated by prime mover 140. UUV 330 begins its ascent in the water body during stage D.

As UUV 330 continues its ascent from a given depth in the water body, ambient hydrostatic pressure 160 decreases. When ambient hydrostatic pressure 160 drops below a first predetermined pressure threshold, low pressure differential valve 145 is actuated. The first predetermined pressure threshold is lower than the gas pressure in recirculation gas tank 120. The actuation of low pressure differential valve 145 causes the gas from recirculation tank 120 to enter first compartment 142 of fluid decoupler 150 and push piston 146 toward second compartment, thereby expelling the seawater from second compartment 144. The gas flow from recirculation gas tank 120 to first compartment 142 depressurizes recirculation gas tank 120 as the volume available for the gas in first compartment 142 increases.

As the gas pressure in the recirculation gas tank 120 falls below a second predetermined pressure threshold, valve 115 is actuated to permit the flow of the gas from low pressure gas tank 110 to recirculation gas tank 120. The second predetermined pressure threshold is lower than the gas pressure in low pressure gas tank 110. The actuation of valve 115, thus, depressurizes low pressure gas tank 110, as the gas flows from low pressure gas tank 110 to recirculation gas tank 120. Thus, when UUV 330 reaches stage E, the low pressure gas tank 110 is depressurized and a bulk of the gas in system 100 is stored in the recirculation tank 120. It will be understood that at stage E, when low pressure gas tank 110 is depressurized, the seawater is expelled from second compartment 144, thereby reducing the ballasting effect of second compartment 144. Thus, it may be advantageous to maneuver UUV 330, after depressurizing at or near surface 310, because the relatively lighter weight of UUV 330 requires relatively less energy to accelerate UUV 330. Likewise, during stage B, maneuvering of UUV 330 may be more energy cost-efficient if performed before the pressurization of high pressure gas tank 130 because the seawater has not yet entered second compartment 144.

During the ascent of UUV 330, during stage D, the temperature of the ambient seawater tends to increase as the UUV 330 approaches surface 310 of the water body. The relatively warmer seawater may be used to increase the temperature of the gas stored in low pressure gas tank 110. As is known in the art, for a constant mass and a constant volume, an increase in temperature of a gas results in an increase in the pressure of a gas, per the ideal gas law. Thus, as the temperature of the gas stored in low pressure gas tank 110 increases, the pressure of the stored gas also increases. Valve 115 may be selectively actuated to depressurize low pressure gas tank 110 by permitting the gas to move from low pressure gas tank 110 to recirculation gas tank 120. Further, if prime mover 140 is operated during stages D and E, the pressure of the gas drops in high pressure gas tank 130, as the high pressure gas stored therein is allowed to move from high pressure gas tank 130 to prime mover 140. The relatively warmer ambient surface seawater flowing through heat exchanger 132 may be used to heat the remaining gas in high pressure gas tank 130, thereby raising the temperature and the pressure of the remaining gas in high pressure gas tank 130. Additionally, the heat generated by the electronics in UUV 330 may also be used to raise the temperature of the gas stored in high pressure gas tank 130. Thus, the relatively higher ambient seawater temperatures may be advantageously used to move higher quantities of gas from low pressure gas tank 110 to recirculation gas tank 120.

In a CPUUV, the buoyancy modulation system modulates the buoyancy of the CPUUV by regulating the amount of seawater in the ballast tank. Since the ambient water is also accumulated in, and displaced out of, second compartment 144, second compartment 144 also acts as a ballast as the total CPUUV mass increases and decreases with the movement of the seawater in and out of second compartment 144. However, this increase and decrease in the total CPUUV mass may operate either to amplify or to counter the buoyancy modulation by the CPUUV's primary buoyancy modulation system during different stages of operation of the CPUUV. For example, when the CPUUV ascends in the water body (during stage D of FIG. 3), the seawater is displaced out of second compartment 144 to depressurize low pressure gas tank 110, as well as out of the CPUUV's main ballast tank which is ejecting the ambient seawater to increase the buoyancy of the CPUUV by decreasing the CPUUV mass. Likewise, when the CPUUV descends in the water body (during stage B of FIG. 3), the seawater is accumulated in second compartment 144 to pressurize recirculation gas tank 120 and high pressure gas tank 130, as well as in the CPUUV's main ballast tank which is accumulating water to decrease the buoyancy of the CPUUV by increasing the CPUUV mass. Thus, during stages B and D, second compartment 144 operates to amplify the buoyancy modulation effect of the CPUUV's primary buoyancy module.

When the CPUUV is starting its ascent (stages C and D of FIG. 3), on the other hand, second compartment 144 operates to counter the buoyancy modulation effect of the CPUUV's primary buoyancy modulation system. For example, as the seawater is ejected out of the main ballast tank to decrease the mass of the CPUUV, second compartment 144 still stores the seawater to harvest the ambient hydrostatic pressure. Such storage of the seawater in second compartment 144 delays the increase in the buoyancy of the CPUUV. Similarly, when the CPUUV is starting its descent (stages A and B of FIG. 3), as the seawater is received into the main ballast to increase the mass of the UUV, second compartment 144 is not yet receiving additional seawater therein (because of the low ambient hydrostatic pressure), thereby delaying the decrease in the buoyancy of the CPUUV. It will, therefore, be understood that the CPUUV's buoyancy modulation system may be suitably configured to take into account the amplifying as well as countering effects of second compartment 144. For instance, the displaceable mass of the seawater in and out of second compartment 144 may be configured to be significantly less than the CPUUV's primary buoyancy modulation system's extent of mass displacement to reduce the ballasting effect of second compartment 144. It will, therefore, be appreciated by one skilled in the art that the relative sizes (i.e., volumes) of second compartment 144 and the main ballast tank act as a constraint in the design of both, second compartment 144 as well as the main ballast tank. For instance, at a certain size or volume of second compartment 144 relative to the main ballast tank, the primary buoyancy modulation system of the CPUUV may be rendered inoperative.

Referring now to FIG. 4, there is illustrated an operational flow for harvesting ambient hydrostatic pressure using system 100 (of FIG. 1) in UUV 330 (of FIG. 3). At block 410, a gas is pressurized in a high pressure gas tank 130 (of FIG. 1) using relatively high ambient hydrostatic pressure 160 (of FIG. 1). As UUV 330 (of FIG. 3) descends in a water body, high pressure differential valve 155 (of FIG. 1) is actuated to pressurize the gas in recirculation gas tank 120 (of FIG. 1) using ambient hydrostatic pressure 160. Valve 125 (of FIG. 1) is then actuated to permit the gas flow from recirculation gas tank 120 (of FIG. 1) to high pressure gas tank 130 (of FIG. 1), thereby pressurizing the gas in high pressure gas tank 130 (of FIG. 1). At block 420, pressurized gas from high pressure gas tank 130 (of FIG. 1) is caused to flow to prime mover 140 (of FIG. 1) by actuation of valve 135 (of FIG. 1). In an embodiment of the invention, prime mover 140 (of FIG. 1) converts the pressure energy of the gas into mechanical work. At block 430, the gas expressed from prime mover 140 (of FIG. 1) is stored in low pressure gas tank 110 (of FIG. 1), thereby increasing the gas pressure in low pressure gas tank 110 (of FIG. 1). At block 440, low pressure gas tank 110 (of FIG. 1) is depressurized at relatively low ambient hydrostatic pressure 160 (of FIG. 1). When UUV 330 (of FIG. 3) is in relatively shallow waters at low ambient hydrostatic pressure 160 (of FIG. 1), low pressure differential valve 145 may be actuated to depressurize recirculation gas tank 120 (of FIG. 1) and valve 115 may actuated to depressurize low pressure gas tank 110 (of FIG. 1).

In an exemplary embodiment, prime mover 140 may be coupled to an impeller (not shown) mounted on the exterior of UUV 330. As UUV 330 is ascending or descending in a water body, responsive to the buoyancy modulation by the primary buoyancy modulation system of UUV 330, the impeller would be driven by the motion of UUV 330 through the water. In an exemplary configuration, the impeller may be operatively coupled to a compressor (not shown) in fluid communication with low pressure gas tank 110 and high pressure gas tank 130. The compressor may pressurize and transfer at least some amount of gas from low pressure gas tank 110 to high pressure gas tank 130.

An advantage of compressed gas system 100 (of FIG. 1) is that a high ambient hydrostatic pressure may be harvested in the form of gas pressure stored in high pressure gas tank 130 (of FIG. 1). The pressurized gas of high pressure gas tank 130 may be used by prime mover 140 (of FIG. 1) by way of non-limiting example only, to, perform mechanical work or to generate power which may be used to operate UUV 330 (of FIG. 3). Thus, no fuel is required for performing mechanical work or generating power. A further advantage of system 100 is the low number of moving parts, limited only to prime mover 140 (of FIG. 1), valves 115, 125, 135, 145, 155 (of FIG. 1) and piston 146 (of FIG. 2). Yet another advantage of system 100 is that no pollutants are emitted in the water body, since system 100 is a closed system. The ambient hydrostatic pressure is, thus, harvested in every cycle of UUV 330 (of FIG. 3) during the descent in the water body and the excess pressure energy is removed from system 100 during the ascent of UUV 330 (of FIG. 3) in the water body.

System for Pressurized Electrolysis For A UUV

Referring to FIG. 5, a pressurized electrolysis system 500 for an UUV is described, according to an embodiment of the invention. System 500 includes a fluid decoupler 520, a variable pressure fresh water tank 530, an electrolyzer 540, a battery 550, a high pressure hydrogen tank 560, a high pressure oxygen tank 570 and a combustor 580. Variable pressure fresh water tank 530 is in fluid communication with electrolyzer 540 via a valve 532. Electrolyzer 540 is in fluid communication with high pressure hydrogen tank 560 via a first one-way differential valve 562 and with high pressure oxygen tank 570 via a second one-way differential valve 572. Each of high pressure hydrogen tank 560 and high pressure oxygen tank 570 is in fluid communication with combustor 580 via check valves 564 and 574, respectively. In one configuration, system 500 may also include a controller (not shown) similar to controller 170 for controlling the operation of one or more of electrolyzer 540, one-way differential valves 562, 572, check valves 564, 574 and combustor 580. System 500 may also include a plurality of sensors (not shown), in communication with a controller (not shown but similar to controller 170 of FIG. 1) for monitoring the temperature within combustor 580 and the quantity of the seawater in impulse water jet engine 600 (of FIG. 6).

In an exemplary embodiment, system 500 further includes a heat exchanger 565 associated with high pressure hydrogen gas tank 560, a heat exchanger 575 associated with high pressure oxygen gas tank 570, a heat exchanger 585 associated with combustor 580 and a coolant pump 587. Heat exchangers 565, 575, 585 and pump 587 are interconnected (via appropriate piping systems) to define a closed loop system. A coolant may be circulated by pump 587 in the closed loop such that heat is extracted from combustor 580, thereby cooling down combustor 580. The extracted heat is transferred by the coolant to high pressure hydrogen tank 560 and high pressure oxygen tank 570 via heat exchangers 565, 575, respectively, thereby heating the gas stored in tanks 560, 570. In an exemplary embodiment, coolant pump 587 may be driven by battery 550 or prime mover 140 (of FIG. 1). Since such coolants and heat transfer systems are known in the art, they are not described in further detail for the sake of brevity.

In one configuration, battery 550 may store the electrical energy generated by prime mover 140 (of FIG. 1). In another embodiment, an ultracapacitor (not shown) may store the electrical energy generated by prime mover 140 (of FIG. 1).

In an exemplary embodiment, high pressure hydrogen tank 560, high pressure oxygen tank 570 and pipes connecting electrolyzer 540 and high pressure gas tanks 560, 570 may be fabricated using strong, light weight carbon composites. In one configuration, high pressure hydrogen tank 560 and the pipe connecting electrolyzer 540 to tank 560 may be coated with a metal on their interior surfaces to prevent leakage of the hydrogen gas through the walls of tank 560 and the pipes connected thereto.

Operation of system 500 is described with reference to FIGS. 3 and 5. At stage A, when UUV 330 is at or near surface 310 of the water body, variable pressure fresh water tank 530 may be filled with fresh water. It is understood that the term “fresh water” includes any distilled or substantially pure water, in contrast with the seawater. In one configuration, fresh water may be collected by collecting atmospheric condensate at surface 310. In another configuration, fresh water may be collected at depth by employing reverse osmosis devices known in the art. During stage B, as UUV 330 begins its descent into the water body towards bed 320, ambient hydrostatic pressure 510 on UUV 330 increases. Relatively high ambient hydrostatic pressure 510 is used to pressurize the fresh water stored in variable pressure fresh water tank 530. As UUV 330 reaches its desired depth, at stage C, the water pressure reaches a desired target (e.g. a maximum) pressure in variable pressure fresh water tank 530. Once the water pressure in variable pressure fresh water tank 530 exceeds a first predetermined pressure threshold, valve 532 is actuated to permit the pressurized fresh water to flow into electrolyzer 540.

With the aid of battery 550, the pressurized fresh water is electrolyzed in electrolyzer 540 to produce pressurized hydrogen gas and pressurized oxygen gas. As will be understood by one skilled in the art, the pressurized hydrogen gas and the pressurized oxygen gas will be at a pressure slightly less, for example, about five percent (5%) less than the pressure of the pressurized fresh water due to the pressure losses associated with, for example, fluid decoupler 520, variable pressure fresh water tank 530 and other components of system 500. One-way differential valves 562, 572 are actuated to permit the flow of pressurized hydrogen gas and oxygen gas from electrolyzer 540 to high pressure hydrogen tank 560 and high pressure oxygen tank 570 respectively. The pressurized hydrogen gas and oxygen gas are then stored in the respective tanks 560, 570.

As is known in the art, as a result of electrolysis, the pressurized hydrogen and oxygen gases are at a higher temperature than the fresh water which was electrolyzed to produce these gases. In an embodiment of the invention, the pressurized hydrogen and oxygen gases stored in respective high pressure gas tanks 560, 570 may be cooled to reduce their temperatures. In one configuration, cold ambient seawater at the stage C, for example, of UUV 330 may be used to extract heat energy from the pressurized hydrogen and oxygen gases stored in respective tanks 560, 570. In another configuration, a coolant may be circulated in thermal coupling with tanks 560, 570 to extract heat energy from the pressurized hydrogen and oxygen gases stored therein. The coolant may be circulated using pumps powered by prime mover 140 (of FIG. 1). As is known in the art, at a constant volume and a constant mass, a drop in temperature of a gas causes a drop in the pressure of a gas, per the ideal gas law. Therefore, the cooling of the pressurized hydrogen and oxygen gases stored in respective high pressure gas tanks 560, 570 causes depressurization of the hydrogen and oxygen gases. This depressurization permits further storage of pressurized hydrogen and oxygen gases in respective tanks 560, 570. Thus, as will be appreciated by one skilled in the art, reducing the temperatures of pressurized hydrogen and oxygen gases permits storage of more quantities of hydrogen and oxygen gases in their respective tanks 560, 570, thereby reducing energy cost per unit of the gases stored in tanks 560, 570.

Referring now to FIGS. 5 and 6, pressurized hydrogen and oxygen gases stored in respective tanks 560, 570 may be injected in combustor 580. The flow of the pressurized hydrogen and oxygen gas may be controlled via respective valves 564, 574. It is understood that the pressure of the hydrogen and oxygen gases injected into combustor 580 is higher than the ambient hydrostatic pressure for effective performance of impulse water-jet engine 600. For instance, at about a depth of about 800 meters (m), the ambient hydrostatic pressure is about 80 atmospheric pressures (atm). At the depth of about 800 m, the pressurized hydrogen and oxygen gases may be injected into combustor 580 at a pressure of about 100 atm, according to an embodiment of the invention.

In one configuration, the pressurized hydrogen and oxygen gases may be fed to a propulsion system, such as described in commonly owned U.S. Pat. No. 7,128,624, issued Oct. 31, 2006, which is incorporated by reference herein in its entirety. In the open cycle underwater propulsion system described in the '624 patent, the pressurized hydrogen and oxygen gases are fed into a combustion chamber to initiate a combustion reaction, which generates high-pressure steam. The high-pressure steam may be cooled with the injection of seawater, as well as due to the expansion of the steam. High-pressure water is then ejected out of the combustor in the form of a water jet, thereby generating thrust for the underwater vehicle. The steam pressure drops due to the expansion of the steam as well as due to the condensation of the steam. As the pressure in the seawater barrel drops, the flapper valve opens to fill the seawater barrel with the ambient seawater.

As the pressurized hydrogen and oxygen gases from their respective tanks 560, 570 are injected into combustor 580, the pressures of the remaining hydrogen and oxygen gases in the respective tanks 560, 570 start to decline. Once the pressures of the hydrogen and oxygen gases in their respective tanks 560, 570 fall below a predetermined threshold, further injection of hydrogen and oxygen gases into combustor 580 would not produce steam sufficiently pressurized to effectively operate water-jet engine 600. Therefore, when the pressures of the hydrogen and oxygen gases in their respective tanks 560, 570 fall below a predetermined threshold, water-jet engine 600 ceases to operate. If, however, the pressure of the hydrogen and oxygen gases remaining in their respective tanks 560, 570 can be increased, the quantities of the hydrogen and oxygen gases that can be usefully injected into combustor 580 may also be increased, thereby increasing the efficiency of system 500 and prolonging the operational times of water-jet engine 600.

In an exemplary embodiment, the hydrogen and oxygen gases remaining in their respective tanks 560, 570 may be further pressurized by heating the stored hydrogen and oxygen gases in their respective tanks 560, 570. As is known in the art, at a constant mass and a constant volume, an increase in temperature results in an increase in pressure for a gas, per the ideal gas law. In one configuration, such heating of the stored hydrogen and gases in their respective tanks 560, 570 may be achieved by transferring heat from combustor 580. Such a transfer of heat from combustor 580 also advantageously cools down combustor 580, thereby reducing the operational stresses thereon and prolonging the operational life of combustor 580. Since heat transfer systems for transferring heat from such a combustor 580 to tanks 560, 570 are known in the art, they are not described in any detail for the sake of brevity.

Referring now to FIG. 6, impulse water-jet engine 600 includes a high pressure housing 610, a nozzle 620 and a flapper valve 630. Nozzle 620 is disposed on one end 612 of housing 610, whereas flapper valve 630 is disposed at the other end 614 of housing 610, opposite to end 612. Flapper valve 630 is actuated to permit the flow of ambient seawater into housing 610. When pressurized hydrogen and oxygen gases combust in combustor 580, high pressures are exerted on the seawater contained in housing 610. In one configuration, a pressure as high as 5000 pounds per square inches (psi) may be exerted on the seawater contained in housing 610. Such high pressure causes flapper valve 630 to shut off, on one hand, and causes a jet of water to be expelled from nozzle 620, on the other hand. The water jet expelled from nozzle 620 provides the propulsion power to UUV 330. As the water jet is expelled from nozzle 620, housing 610 is depressurized. This depressurization of housing 610 causes flapper valve 630 to open and permit further flow of the ambient seawater into housing 610.

Referring to FIG. 7, a process flow 700 for pressurized electrolysis in an underwater vehicle is described. At block 710, the fresh water stored in a variable pressure fresh water tank 530 (of FIG. 5) is pressurized using ambient hydrostatic pressure 510. Pressurized fresh water is electrolyzed in electrolyzer 540 (of FIG. 5) to generate pressurized hydrogen gas and oxygen gas, at block 720. At block 730, the pressurized hydrogen and oxygen gases are stored in respective high pressure gas tanks 560, 570 (of FIG. 5). At block 740, the pressurized hydrogen and oxygen gases stored in respective tanks 560, 570 are injected in combustor 580 (of FIG. 5). The combustion of pressurized hydrogen and oxygen gases in combustor 580 (of FIG. 5) generates propulsion power for UUV 330 (of FIG. 3) by expelling water jets from impulse water jet engine 600 (of FIG. 6).

An advantage of system 500 is that ambient hydrostatic pressure is harvested to pressurize the freshwater, which, when electrolyzed, produces pressurized hydrogen and oxygen gases. Therefore, the need for pumping energy generally required to pressurize the hydrogen and oxygen gases is eliminated. Another advantage of system 500 is that sufficient thrust power may be generated to enable UUV 330 to sprint at a speed of about forty (40) knots. UUV 330 equipped with system 500 may be capable of sprints ranging from about 1 kiloyard (kyd) to about 5 kyd. However, system 500 may be used for electrolysis only when the ambient hydrostatic pressure exerted on the fresh water is sufficiently high to produce pressurized hydrogen and oxygen gases. Thus, system 500 may be effective only at depths below a threshold depth. Furthermore, as the size of UUV 330 (of FIG. 3) increases, the amount of pressurized hydrogen and oxygen gases required to provide sufficient propulsion power also increases. Generation of this increased amount of pressurized hydrogen and oxygen gases via electrolysis requires more electric energy. Such increased electric energy requirements necessitates a battery 550 with one or more of increased size and power rating, particularly when the electrolysis can occur only during stage C (of FIG. 3), for example, of UUV 330 (of FIG. 3).

System for Continuous Pressurized Electrolysis

Referring now to FIG. 8, a system 800 for substantially continuous pressurized electrolysis is illustrated, according to an embodiment of the invention. System 800 provides for continuous pressurized electrolysis in UUV 330 (of FIG. 3), regardless of the depth of UUV 330 (of FIG. 3) in the water body. Since the electrolysis is not limited only to depths below a threshold depth, battery 550 may be reduced in one or more of size and power rating than that compared to when the electrolysis is limited only at depths exceeding a certain threshold depth. For example, non-continuous electrolysis of a given amount of water in a relatively shorter duration requires a battery capable of delivering higher amounts of power in the relatively short duration. Continuous electrolysis, on the other hand, for the same given amount of water over a relatively longer duration may be achieved by using a battery of reduced size and/or power rating, which may deliver relatively lower power over the longer period of time. System 800 includes a variable pressure fresh water tank 530, a variable pressure hydrogen tank 820 and a variable pressure oxygen tank 830. System 800 may also include a controller (not shown, but similar to controller 170 (of FIG. 1)) in electrical communication with one or more pressure sensors (not shown) disposed in variable pressure tanks 530, 820, 830, high pressure tanks 810, 560, 570 and fluid decoupler 520.

As shown in FIG. 8, fluid decoupler 520 is subject to ambient hydrostatic pressure 510 and is in further in fluid communication with each of variable pressure tanks 530, 820, 830. Particularly, fluid decoupler 520 is in fluid communication with variable pressure fresh water tank 530 via a pressure transfer system 805; with variable pressure hydrogen tank 820 via a pressure transfer system 815; and with variable pressure oxygen tank 830 via a pressure transfer system 825. In one configuration, pressure transfer systems 825, 815, 825 may take the form of a hydraulic fluid system with piston and cylinder arrangement, as known in the art. For instance, the ambient hydrostatic pressure exerted on the fluids of systems 805, 815, 825 may be selectively transferred to the fresh water stored in variable pressure fresh water tank 530, the hydrogen gas stored in variable pressure hydrogen tank 820 and the oxygen gas stored in variable pressure oxygen tank 830 respectively.

Variable pressure fresh water tank 530 is in fluid communication with a high pressure fresh water tank 810 via a one-way differential water valve 835. Similarly, variable pressure hydrogen tank 820 is in fluid communication with high pressure hydrogen tank 560 via a one-way differential gas valve 562 and variable pressure oxygen tank 830 is in fluid communication with high pressure oxygen tank 570 via one-way differential gas valve 564. High pressure water tank 810 is in fluid communication with electrolyzer 540 via a check valve 845 (e.g., either self-actuated or controlled by a controller). Check valve 845 regulates the flow of the pressurized water from high pressure water tank 810 to electrolyzer 540. Electrolyzer 540 is in fluid communication with each of variable pressure hydrogen tank 820 and variable pressure oxygen tank 830. Variable pressure hydrogen tank 820 and variable pressure oxygen tank 830 are in fluid communication with high pressure hydrogen tank 560 and high pressure oxygen tank 570 respectively.

Pressure transfer system 805 may be actuated to exert ambient hydrostatic pressure 510 on the fresh water stored in variable pressure fresh water tank 530. Once the water pressure in variable pressure fresh water tank 530 exceeds a predetermined threshold, one-way differential valve 835 may be actuated to permit the flow of pressurized water to high pressure water tank 810. One-way differential valve 835 prevents the reverse flow of pressurized water from high pressure water tank 810 to variable pressure water tank 530. In this embodiment, high pressure water is available for electrolysis even when UUV 330 (of FIG. 3) is in shallow waters with relatively low ambient hydrostatic pressure. In contrast, in system 500, high pressure water is available for electrolysis only when UUV 330 (of FIG. 3) is below a depth threshold with relatively high ambient hydrostatic pressure 160 (of FIG. 1).

The hydrogen and oxygen gases released from the electrolysis of high pressure water in electrolyzer 540 are stored in variable pressure hydrogen tank 820 and variable pressure oxygen tank 830 respectively. When UUV 330 (of FIG. 3) descends below a threshold depth, relatively high ambient hydrostatic pressure 510 may be used to augment the pressure of the hydrogen and the oxygen gases stored in respective tanks 820, 830. As the hydrogen and oxygen pressures exceed predetermined pressure thresholds, respective one-way differential valves 562, 572 are actuated to permit the flow of the pressurized hydrogen and oxygen gases to high pressure hydrogen and oxygen tanks 860, 570 respectively. One-way valves 562, 572 prevent the reverse flow of pressurized gases from high pressure gas tanks 560, 570 to respective variable pressure tanks 820, 830.

An advantage of system 800 is that electrolysis of fresh water may be performed continuously regardless of the depth of UUV 330 (of FIG. 3). Therefore, increased quantities of pressurized hydrogen and oxygen gases may be generated by system 800 as compared to those generated by system 500, without corresponding increase in the size of battery 550.

While the foregoing invention has been described with reference to the above-described embodiment, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims. Accordingly, the specification and the drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations of variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. 

1. A method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle, said method comprising the steps of: pressurizing a gas in a first gas tank in the underwater vehicle using a high ambient hydrostatic pressure encountered by the underwater vehicle during a submerged state of the underwater vehicle within a water body; transferring at least some of the pressurized gas from said first gas tank to a second gas tank in the underwater vehicle; transferring at least some amount of the pressurized gas from said second gas tank to a prime mover in the underwater vehicle for performing mechanical work; storing the gas expressed by said prime mover in a third gas tank in the underwater vehicle; transferring at least some amount of the gas from said third gas tank to said first gas tank in the underwater vehicle using a low ambient hydrostatic pressure encountered by the underwater vehicle during the submerged state in the water body.
 2. The method of claim 1, wherein the pressurizing step comprises the step of actuating a first differential valve operatively coupled to the first gas tank and subjected to the ambient hydrostatic pressure, when the underwater vehicle is submerged in the water body, thereby subjecting the gas contained in the first gas tank to the ambient hydrostatic pressure.
 3. The method of claim 1, further comprising the step of depressurizing the first gas tank by subjecting the gas contained therein to an ambient hydrostatic pressure lower than the gas pressure in the first gas tank by actuating a second differential valve operatively coupled to the first gas tank and subjected to the ambient hydrostatic pressure.
 4. The method of claim 3, further comprising the step of depressurizing the third gas tank by actuating a first valve disposed between the third gas tank and the first gas tank when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank, thereby causing a transfer of at least some amount of gas from the third gas tank to the first gas tank.
 5. The method of claim 1, further comprising a step of cooling the gas stored in said second gas tank using the ambient water when the underwater vehicle is in the submerged state within the water body where the temperature of the ambient water is lower than the temperature of the gas stored in said second gas tank.
 6. The method of claim 1, further comprising a step of heating the gas stored in said third gas tank using the ambient water when the underwater vehicle is in a submerged stated within the water body where the temperature of the ambient water is higher than the temperature of the gas stored in said third gas tank.
 7. The method of claim 1, further comprising a step of heating the gas stored in said second gas tank when said prime mover is in operation.
 8. The method of claim 1, further comprising a step of cooling the gas stored in said third gas tank when said prime mover is in operation.
 9. A compressed gas system for harvesting ambient hydrostatic pressure for an underwater vehicle operative to descend within a water body to a given depth and to ascend from the given depth in an alternating fashion, said system comprising: a first gas tank; a second tank in fluid communication with the first gas tank; a third gas tank in fluid communication with the second gas tank and the first gas tank; a first valve for controlling a gas flow between the second gas tank and the third gas tank; and a second valve for controlling a gas flow between the third gas tank and the first gas tank, wherein gas stored in the third gas tank is selectively subjectable to the ambient hydrostatic pressure during a submerged state of the underwater vehicle within the water body.
 10. The system of claim 9, further comprising: a first differential valve operatively coupled to said third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank; and a second differential valve operatively coupled to said third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is higher than the gas pressure in the third gas tank.
 11. The system of claim 9, further comprising a fluid decoupler interposed between and in fluid communication with said third gas tank and said first and second differential valves, wherein said fluid decoupler comprises: a piston defining a first and a second compartment in said fluid decoupler; wherein said first compartment is configured to be in fluid communication with said first gas tank; and wherein said second compartment is configured to be in fluid communication with said first and second differential valves.
 12. The system of claim 9, further comprising: a first heat exchanger configured to extract heat energy from the gas stored in said first gas tank; and a second heat exchanger configured to transfer heat energy into the gas stored in said second gas tank.
 13. A method for pressurized electrolysis of fresh water in an underwater vehicle comprising the steps of: storing fresh water in a first water tank in the underwater vehicle; pressurizing the fresh water in the said first water tank using the ambient hydrostatic pressure when said underwater vehicle is in a submerged state within a water body; electrolyzing said pressurized water to release hydrogen gas and oxygen gas; and storing said hydrogen gas and said oxygen gas in a first hydrogen tank and a first oxygen tank respectively.
 14. The method of claim 13, further comprising the step of cooling the stored hydrogen gas in said first hydrogen tank, thereby reducing the pressure of the stored hydrogen gas in said first hydrogen tank.
 15. The method of claim 13, further comprising the step of cooling the stored oxygen gas in said first oxygen tank, thereby reducing the pressure of the stored oxygen gas in said first oxygen tank.
 16. The method of claim 13, further comprising the step of heating the stored oxygen gas and the stored hydrogen gas in said first oxygen tank and said first hydrogen tank, respectively, thereby increasing the pressures of the stored oxygen gas and the stored hydrogen gas in said first oxygen tank and said first hydrogen tank respectively.
 17. The method of claim 13, further comprising the steps of: pressurizing the fresh water stored in said first water tank using the ambient hydrostatic pressure encountered by the underwater vehicle in the submerged state in the water body; and transferring the pressurized water from said first water tank to a second water tank.
 18. The method of claim 13, further comprising the step of storing the hydrogen gas and the oxygen gas released in the electrolyzing step in a second hydrogen tank and a second oxygen gas, respectively, before storing the hydrogen gas and the oxygen gas in said first hydrogen tank and said first oxygen tank, respectively.
 19. The method of claim 18, further comprising the steps of: pressurizing the hydrogen gas and the oxygen gas stored in the second hydrogen tank and the second oxygen tank, respectively, using the ambient hydrostatic pressure in the submerged state of the underwater vehicle within the water body; and transferring said pressurized hydrogen gas and said oxygen gas from said second hydrogen tank and said second oxygen tank, respectively, to said first hydrogen tank and said first oxygen tank, respectively.
 20. A system of pressurized electrolysis of fresh water in an underwater vehicle comprising: a first fresh water tank; an electrolyzer in fluid communication with said first fresh water tank, said electrolyzer configured to electrolyze fresh water to release hydrogen and oxygen gases; a first hydrogen tank and a first oxygen tank in fluid communication with said electrolyzer for respectively storing the hydrogen gas and the oxygen gas released by said electrolyzer; and a first pressure transfer system configured to exert the ambient hydrostatic pressure on the fresh water stored in said first fresh water tank.
 21. The system of claim 20, further comprising: a first one-way differential valve interposed between said electrolyzer and said first hydrogen tank; and a second one-way differential valve interposed between said electrolyzer and said first oxygen tank.
 22. The system of claim 21, further comprising: a second fresh water tank in fluid communication with said first fresh water tank via a third one-way differential valve, and with said electrolyzer via a first valve; a second hydrogen tank in fluid communication with said electrolyzer via a second valve, and with said first hydrogen tank via said first one-way differential valve; a second oxygen tank in fluid communication with said electrolyzer via a third valve, and with said first oxygen tank via said second one-way differential valve; a second pressure transfer system adapted to exert the ambient hydrostatic pressure on the hydrogen stored in said second hydrogen tank, in the submerged state of the underwater vehicle within the water body; and a third pressure transfer system adapted to exert ambient hydrostatic pressure on the oxygen stored in said second oxygen tank, in the submerged state of the underwater vehicle within the water body.
 23. The system of claim 22, further comprising a combustor configured to receive from said first hydrogen tank, the pressurized hydrogen gas, and, from said first oxygen tank, the pressurized oxygen gas for combustion therein.
 24. The system of claim 23, further comprising a heat transfer system configured to transfer at least some amount of heat, generated in said combustor due to the combustion of the pressurized hydrogen gas and the pressurized oxygen gas therein, to said first hydrogen tank and said first oxygen tank, thereby raising the temperatures and the pressures of the hydrogen gas and the oxygen gas stored in the respective first hydrogen and oxygen tanks. 